Treatment pattern monitor

ABSTRACT

The invention relates to an apparatus and a method for determining the applicability of a treatment pattern for manipulation of a cornea of an eye using a laser. The concept of the present invention is based on the determination of an actual volumetric profile based on a set of input data and a theoretical volumetric profile which is created independently based on only the basic optical parameters. On the basis of a comparison of the determined volumetric profiles it is determined whether the actual volumetric profile is within predetermined tolerances.

This is a continuation of International Application PCT/EP2009/057372,with an international filing date of Jun. 15, 2009, and which claims thebenefit of German Application No. 10 2008 028 509.9, with a foreignfiling date of Jun. 16, 2008.

FIELD OF INVENTION

The invention relates to an apparatus and a method for determining theapplicability of a treatment pattern for manipulation of a cornea of aneye using a laser. In particular, a treatment to reduce a refractiveerror of an eye is verified by using independent measures to be withincertain tolerances before the actual treatment of the eye.

BACKGROUND OF THE INVENTION

The typical course of the planning phase for a refractive treatmentincludes, i.a., the upload of input data corresponding to a desiredrefractive correction, specification of the desired correction, creationof the treatment pattern, and upload of the data onto a therapeuticplatform, i.e. a laser treatment system. The desired refractivecorrection may be based on diagnostic data obtained by at least one of asubjective refractive error and a measured objective refractive error.The measured refractive error may be obtained by at least one of awavefront sensor, topographical measurement device or a pachymetrymeasurement device. Low order aberrations may be determined by asubjective refractive error, e.g. considering the verbal feedback of apatient.

The generated corneal shape change profile, e.g. a simulated ablationpattern of an excimer laser or a volumetric femtosecond removal profile,may be disclosed in a graphical user interface GUI or an otherimplementation. The volumetric profile describes the amount of micronsof corneal tissue which is planned to be removed in a certain 3dimensional location on or in the cornea. Tissue on the cornea, i.e., onthe surface of the cornea may be removed, e.g., by an excimer laser andtissue in the cornea, i.e., an intrastromal effect may be caused by afemtosecond laser.

In the determination of a refractive treatment checks may be applied,e.g., whether the corneal thickness after a treatment is stillsufficient such that the treatment is applicable. In presently availablesystems the person controlling a treatment apparatus, usually aphysician, finally decides whether a treatment is conducted, i.a., basedon a GUI or an other implementation as outlined above.

One of the continuously developing usability and regulatory requirementsis to ensure a certain level of usability comfort and applicable safetyto the user, i.e., to make refractive treatments safe and more reliableand demonstrate this in an easy but quantitative way to the user. Thesole observation of simulated ablation patterns may not be sufficientany more for future applications.

There is a need to provide an independent check that the createdablation pattern is actually related to the desired refractivecorrection.

Document WO-A-98/40041, from Chiron Technolas GmbH OphthalmologischeSysteme, relates to a simulation of a laser treatment on the eye bypretreating a contact lens. The treated contact lens is placed on thepatient's eye and the patient's resulting visual acuity is measured. Ifwithin acceptable limits, the treatment is then performed on thepatient's eye. Otherwise, the treatment pattern is adjusted.

An aspect of the invention is to provide a method and an apparatus fordetermining whether the volumetric ablation relating to a certaintreatment pattern is within predefined tolerances, i.e., to provide anindependent check of the applicability of the created volumetricprofile.

SUMMARY

The above objects are achieved by the features of the appended claims.Aspects of the invention are directed to a method and an apparatus fordetermining the applicability of a treatment pattern for manipulation ofthe cornea of an eye using a laser, e.g. an excimer laser and/or afemtosecond laser. Further, the invention relates to a treatment patterncalculator and a laser treatment system. The concept of the presentinvention is based on the determination of an actual volumetric profileand a theoretical volumetric profile, each based on the same data, whichcorrespond to a desired treatment. In particular, the theoreticalvolumetric profile may be based on one, more or all data from which theactual volumetric profile is determined.

On the basis of a comparison of the actual and the theoreticalvolumetric profile it is determined whether the actual volumetricprofile is within predetermined tolerances, i.e. whether the plannedtreatment is actually related to the desired refractive correction of aneye. Only when this check is satisfactory the treatment pattern is usedfor performing a treatment of the eye. The method may be implementedinto a refractive device, e.g. a treatment system and/or a treatmentpattern calculator, to provide an independent check of the createdvolumetric profile.

According to one aspect, a treatment pattern is developed based on a setof input data corresponding to a desired refractive correction. Anactual volumetric profile is determined based on said treatment pattern.Further, a theoretical volumetric profile is determined based on atleast one of said set of input data by using a basic theoretical model.In other words, the theoretical volumetric profile is based on at leasta part of the same data as the actual volumetric profile, preferablybased on only the basic optical parameters. However, the theoreticalvolumetric profile is developed independently from the latter. Forexample, the theoretical volumetric profile may be based on the sphere,the cylinder and/or the optical zone as one of said input data. Theactual volumetric profile is compared with the theoretical volumetricprofile and it is determined whether the actual volumetric profile iswithin specified tolerances on the basis of the theoretical volumetricprofile.

According to the invention a basic theoretical model is generated, e.g.depending on the origin of the volumetric profile, which approximatesthe shape of an actually created volumetric profile. The shape can bedescribed by different parameters such as the maximum ablation depthand/or the central ablation depth and/or the treatment area and/or theablation volume and/or the amount of correction in diopters of thevolumetric pattern and/or the difference and/or ratio of a centralablation depth and an ablation depth in a defined area and/or thedifference and/or ratio of minimum or maximum ablation depth in definedareas.

A slight modification of at least one of these parameters of thetheoretical model creates in minimum two theoretical volumetricprofiles, which may serve as minimum and maximum tolerance limits,so-called estimators, for the actually generated volumetric profile.

Dependent on the spacing, i.e. the difference of the modifiedparameters, more or less detailed statements can be created whichindicate the over or under correction potential of the actuallygenerated volumetric profile. The narrower the spacing of the modifiedparameters, i.e., the smaller the tolerance range, the better the actualeffect of the treatment pattern can be determined. The better the actualeffect of the treatment pattern can be determined, the better apotential treatment error can be identified.

The final outcome of the method/apparatus according to the invention maybe the statement that the generated volumetric profile is applicable/notapplicable and/or is within predefined limits ±X % or ±X Diopters of thedesired treatment or exceeds the predefined limits ±X % or ±X Diopters.

This method can be applied to standard non personalized treatments aswell as to personalized treatments in which certain diagnostic maps suchas wavefront, topography, pachymetry (usefull for femtosecond laserapplications) or combinations of them are used.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative, non-limiting embodiments of the present invention will bedescribed by way of example with reference to the accompanying drawings,in which the same reference number is used to designate the same orsimilar components in different figures, and in which:

FIG. 1 is a block diagram of the method for determining theapplicability of a treatment pattern according to the invention; and

FIG. 2 is a schematic sectional view of a simulated post-operativecornea with a tolerance range according to the invention.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of the method according to the invention.Input data 10 relate to a desired refractive correction. It is notedthat the present invention is not limited to one or more methods fordetermining a desired refractive correction. In fact, the type ofdetermination does not affect the applicability of the presentinvention.

Based on the input data 10, a treatment pattern 12 is developed. Anexemplary simple case is represented in a standard non aspheric excimerlaser treatment pattern such as Bausch & Lomb's PlanoScan orTissueSaving. A typical treatment pattern for these two classes ofablation algorithms may be based on the subjective refraction expressedin subjective sphere S_(subj), subjective cylinder C_(subj), subjectiveaxis of the cylinder A_(subj) and the desired optical zone OZ of thetreatment. In the case of the TissueSaving algorithm additionalparameters such as the central preoperative topographical K-ReadingK_(pre) can be added.

Based on the treatment pattern 12 an actual volumetric profile 14 isdetermined. The actual volumetric profile 14 may represent the amount ofablated corneal tissue to apply a desired refractive correction to acornea of an eye. It is noted that in the context of the presentinvention any refractive manipulation of the eye may be considered fordetermining the applicability of a treatment. Known manipulations are,e.g., ablation by an excimer laser or intrastromal manipulation by afemtosecond laser.

To provide an independent check of the delivered refractive correctionin the case of an application of the treatment pattern 12 to a cornealsurface, an independent estimator is needed. The estimator is determinedindependently of the treatment pattern calculation to evaluate thecontained refractive power, i.e. the amount of correction in diopters D,in the actual volumetric profile 14.

A theoretical volumetric profile 16 is determined based on one, more orall of said input data using a basic theoretical model. For the casesmentioned above (PlanoScan and TissueSaving) a toric or non-toric thinlens formula as basic theoretical model may be an appropriate estimator.With this estimator the above mentioned parameters which describe theshape of the treatment pattern, such as maximum and central ablationdepth, can be derived independently from the actual used PlanoScan orTissueSaving algorithm.

The power, i.e. the amount of correction in diopters D, and the opticalzone of the thin lens formula may be modified successively to provide abest match up to a certain tolerated deviation expressed in dioptres ofspherical equivalent. This may be ±1.0 D, ±0.5 D, ±0.33 D or even ±0.25D.

In the case of the spherical equivalent this range is directly dependenton the amount of desired astigmatic correction, as a rotationallysymmetric profile is used to approximate a toric profile. The opticalzone may be approximated in 1.00 mm steps or even smaller steps such as0.75 mm, 0.50 mm or 0.25 mm.

A more detailed implementation may use tonic estimators to create a setof parameters to describe the shape of upper and lower limits. Theactual volumetric profile 14 must be within the two created lower andhigher estimators. Having this condition creates a simple decisionprocess, based on a comparison 18 of the actual volumetric profile 14with the theoretical volumetric profile 16, whether the created ablationprofile is within the pre specified tolerances of the desired correctionor not, i.e., whether the determined treatment pattern 12 relating tothe actual volumetric profile 14 is applicable or not.

In general, two different strategies may be considered to create astatement about the contained power, i.e. the amount of correction indiopters D, in an actual volumetric profile 14.

First Strategy (Fixed Tolerance)

FIG. 2 shows a predefined tolerance range 22, which may be used toevaluate whether the created actual volumetric profile 14, leading to apost-operative corneal surface 20, is consistently within this tolerancerange. In the first strategy fixed threshold values may be used for atleast one of the tolerated deviation in sphere ΔS_(subj), cylinderΔC_(subj), axis of the cylinder ΔA_(subj) and the desired optical zoneΔOZ.

A lower Estimator can be given by the following parameters:

S _(subj, low) =S _(subj) −ΔS _(subj)

C _(subj, low) =C _(subj) −ΔC _(subj)

A_(subj, low)=A_(subj)

OZ_(low)=OZ−ΔOZ

The higher Estimator can be given by the following parameters:

S _(subj, high) =S _(subj) +ΔS _(subj)

C _(subj, high) =C _(subj) +ΔC _(subj)

A_(subj, high)=A_(subj)

OZ_(high)=OZ+ΔOZ

According to this example the values for sphere, cylinder and opticalzone may be changed at the same time to get the lower and higherestimator. Overall different combinations of values might be changed tocreate the estimators. Only sphere might be changed and cylinder andoptical zone might be unchanged, only optical zone might be changed andthe refraction unchanged, axis of cylinder might be changed and allother values unchanged. Thus, at least one of the before mentionedvariables may be changed.

According to an aspect of the invention it is determined whether theactual volumetric profile 14 is within the two created lower and higherestimators defining the predefined tolerance range 22. Based on thecomparison 18 a statement is created that the actual volumetric profile14, leading to the post-operative corneal surface 20, does/does notdeliver a refractive correction which is within the accepted tolerances.Also more than one lower and one higher tolerance level can bedetermined to provide a more detailed information about the effect ofthe actual volumetric profile 14.

Second Strategy (Minimal Tolerance)

According to the second strategy, at least one of the threshold valuesfor the tolerated deviation in sphere ΔS_(subj), cylinder ΔC_(subj),axis of the cylinder ΔA_(subj) and the desired optical zone ΔOZ can beoptimised to provide the minimal deviation from the actual ablationprofile, which may be accomplished iteratively (not shown in FIG. 1).

The result from this strategy are minimal detected deviations in sphere,cylinder, axis and optical zone which may still allow an upper and lowerestimation of the refractive power of the actual volumetric profile 14.In particular, in case the comparison 18 provides a difference betweenthe actual volumetric profile 14 and the theoretical volumetric profile16 which is greater than an approximation step of the theoreticalvolumetric profile 16, the latter profile is amended to reduce thetolerance range and compared again with the actual volumetric profile14. In other words, one or more parameters of the theoretical volumetricprofile 14 are successively modified to approximate the theoreticalvolumetric profile (16) to the actual volumetric profile (14).

Both described strategies can be used in more complex ablationprocedures. So in the case of aspheric ablation profiles in which acertain offset on spherical aberration is added to the basic spherocylindrical profile, this component will be added to the theoreticalestimator formula.

In other words the estimator in these cases may be the appropriate thinlens formula plus the pre defined spherical aberration. In even morecomplex ablation strategies such as wavefront driven ablations, a meansphero cylindrical profile using a thin lens formula or in a furtherimplementation an aspheric thin lens formula may be used. In the case ofspecific questions even individual high order components may be used toevaluate for example the total amount of coma or higher order aberrationinformation such like HORMS or 3rd order RMS or 4th order RMS or 5thorder RMS contained in a specific ablation profile.

Both mentioned strategies can also be used to create specific statementson a sub group of parameters down to only one specific parameter. Oneexemplary possibility can be to only check the applicability of atreatment pattern with reference to the delivered optical zone.

It needs to be reiterated, that the invention is not limited to anexcimer laser treatment pattern. As soon as the actual volumetricprofile 14 is given, the estimator can be determined. In a more generalinterpretation of this concept, the estimator may be applied to asimulated post-operative corneal profile, which is given based on thepre-operative diagnostic data (for example from the Next GenerationDiagnostic Instrument NGDI, Bausch & Lomb) and a volumetric ablationprofile given by an excimer laser or a femtosecond laser.

The above described method may be implemented in a treatment calculatoror a laser software where a treatment file is uploaded to provide anindependent check of the outcome of the treatment calculator. Such atreatment calculator or an apparatus for conducting the above method maybe implemented in a laser treatment system, e.g., with an excimer laserand/or a femtosecond laser.

While certain embodiments have been chosen to illustrate the inventionit will be understood by those skilled in the art that changes andmodifications can be made therein without departing from the scope ofthe invention as defined in the appended claims. In particular it isnoted that even though exemplary reference was made to an myopic visionerror also other vision errors will benefit from the present invention.

1. A method for determining the applicability of a treatment pattern formanipulation of a cornea of an eye using a laser, comprising thefollowing steps: (a) developing said treatment pattern using input datacorresponding to a desired refractive correction; (b) determining anactual volumetric profile based on said treatment pattern; (c)determining a theoretical volumetric profile based on at least one ofsaid input data by using a basic theoretical model; and (d) comparingthe actual volumetric profile with the theoretical volumetric profile todetermine whether the actual volumetric profile is within specifiedtolerances on the basis of the theoretical volumetric profile.
 2. Themethod of claim 1, wherein the theoretical model uses a number of basicparameters, further comprising the step of determining a firsttheoretical volumetric profile when using said number of basicparameters of the theoretical model and determining a second theoreticalvolumetric profile using said theoretical model wherein at least one ofsaid number of basic parameters is modified.
 3. The method of claim 2,wherein said actual volumetric profile is compared with said firsttheoretical volumetric profile which serves as a minimum estimator andwherein said actual volumetric profile is compared with said secondtheoretical volumetric profile which serves as a maximum estimator. 4.The method of claim 3, wherein the modification of said at least oneparameter is made to determine a limit of a potential over or undercorrection of the actual volumetric profile.
 5. The method of claim 2,wherein said basic parameters are at least one of the maximum ablationdepth, the central ablation depth, the treatment area, the ablationvolume, the amount of correction in diopters of the volumetric pattern,the difference and/or ratio of a central ablation depth and an ablationdepth in a defined area, or the difference and/or ratio of minimum ormaximum ablation depth in defined areas.
 6. The method of claim 1,wherein the step of determining whether the actual volumetric profile iswithin specified tolerances further comprises determining whether theactual volumetric profile corresponds to the desired refractivecorrection.
 7. The method of claim 1, wherein the basic theoreticalmodel is a toric or nontoric thin lens formula.
 8. The method of claim7, wherein an amount of correction in diopters and/or an optical zone ofthe thin lens formula is modified successively to approximate thetheoretical volumetric profile to the actual volumetric profile.
 9. Themethod of claim 8, wherein the modification step of the amount ofcorrection in diopters is one of ±1.0 D, ±0.5 D, ±0.33 D or ±0.25 D. 10.The method of claim 8, wherein the modification step of the optical zoneis one of 1.00 mm, 0.75 mm, 0.50 mm or 0.25 mm.
 11. The method of claim1, wherein the specified tolerance is a fixed tolerance, preferably atleast one of a tolerated deviation in sphere, cylinder, axis, andoptical zone.
 12. The method of claim 1, wherein the specified toleranceis a minimal tolerance, preferably by optimizing the tolerated deviationin sphere, cylinder, axis and optical zone to provide the minimaldeviation from the actual volumetric profile. 13-15. (canceled)
 16. Themethod of claim 1, wherein the method resides on a processor readablestorage device.
 17. The method of claim 16, wherein the processorreadable storage device is a floppy disk, flexible disk, hard disk,magnetic tape, CD-ROM, DVD, magnetic medium, optical medium, physicalmedium, RAM, PROM, EPROM, or FLASH-EPROM.
 18. A system for determiningthe applicability of a treatment pattern for manipulation of a cornea ofan eye using a laser, comprising: (a) first computer software receivinginput data corresponding to a desired refractive correction anddeveloping a treatment pattern from the input data; (b) second computersoftware receiving the treatment pattern and developing an actualvolumetric profile from the treatment pattern; (c) third computersoftware receiving a theoretical volumetric profile wherein thetheoretical volumetric profile is based on the input data and developedfrom a basic theoretical model; and (d) fourth computer softwareprogrammed to compare the actual volumetric profile with the theoreticalvolumetric profile to determine whether the actual volumetric profile iswithin specified tolerances on the basis of the theoretical volumetricprofile.
 19. The system of claim 18, wherein the theoretical model usesa number of basic parameters, further comprising a fifth computersoftware determining a first theoretical volumetric profile when usingthe basic parameters of the theoretical model and determining a secondtheoretical volumetric profile using said theoretical model wherein atleast one of the number of basic parameters is modified.
 20. The systemof claim 19, said fifth computer software comparing the actualvolumetric profile with the first theoretical volumetric profile whichserves as a minimum estimator and comparing the actual volumetricprofile with the second theoretical volumetric profile which serves as amaximum estimator.
 21. The system of claim 20, said fifth computersoftware modifying at least one of the basic parameters to determine alimit of a potential over or under correction of the actual volumetricprofile.
 22. The system of claim 19, wherein the basic parameters are atleast one of the maximum ablation depth, the central ablation depth, thetreatment area, the ablation volume, the amount of correction indiopters of the volumetric pattern, the difference and/or ratio of acentral ablation depth and an ablation depth in a defined area, or thedifference and/or ratio of minimum or maximum ablation depth in definedareas.
 23. The system of claim 18, said fourth computer softwaredetermining whether the actual volumetric profile corresponds to thedesired refractive correction.
 24. The system of claim 18, wherein thebasic theoretical model is a toric or nontoric thin lens formula. 25.The system of claim 24, further comprising a sixth computer softwaresuccessively modifying an amount of correction in diopters and/or anoptical zone of the thin lens formula to approximate the theoreticalvolumetric profile to the actual volumetric profile.
 26. The system ofclaim 25, wherein the amount of correction in diopters is one of ±1.0 D,±0.5 D, ±0.33 D or ±0.25 D.
 27. The system of claim 25, wherein themodification of the optical zone is one of 1.00 mm, 0.75 mm, 0.50 mm or0.25 mm.
 28. The system of claim 18, wherein the specified tolerance isa fixed tolerance, preferably at least one of a tolerated deviation insphere, cylinder, axis, and optical zone.
 29. The system of claim 18,wherein the specified tolerance is a minimal tolerance, preferably byoptimizing the tolerated deviation in sphere, cylinder, axis and opticalzone to provide the minimal deviation from the actual volumetricprofile.
 30. The system of claim 18, wherein said computer system is alaser treatment system.
 31. The system of claim 18, wherein saidcomputer system includes a treatment calculator.
 32. The system of claim31, wherein the treatment calculator determines a treatment pattern fromdiagnostic data.
 33. One or more processor readable storage deviceshaving processor readable code embodied on said processor readablestorage devices, said processor readable code for programming one ormore processors to execute a method for determining the applicability ofa treatment pattern for manipulation of a cornea of an eye using alaser, comprising the following steps: (a) developing said treatmentpattern using input data corresponding to a desired refractivecorrection; (b) determining an actual volumetric profile based on saidtreatment pattern; (c) determining a theoretical volumetric profilebased on at least one of said input data by using a basic theoreticalmodel; and (d) comparing the actual volumetric profile with thetheoretical volumetric profile to determine whether the actualvolumetric profile is within specified tolerances on the basis of thetheoretical volumetric profile.
 34. The processor readable storagedevice of claim 33, wherein the theoretical model uses a number of basicparameters, further comprising the step of determining a firsttheoretical volumetric profile when using said number of basicparameters of the theoretical model and determining a second theoreticalvolumetric profile using said theoretical model wherein at least one ofsaid number of basic parameters is modified.
 35. The processor readablestorage device of claim 34, wherein said actual volumetric profile iscompared with said first theoretical volumetric profile which serves asa minimum estimator and wherein said actual volumetric profile iscompared with said second theoretical volumetric profile which serves asa maximum estimator.
 36. The processor readable storage device of claim35, wherein the modification of said at least one parameter is made todetermine a limit of a potential over or under correction of the actualvolumetric profile.
 37. The processor readable storage device of claim34, wherein said basic parameters are at least one of the maximumablation depth, the central ablation depth, the treatment area, theablation volume, the amount of correction in diopters of the volumetricpattern, the difference and/or ratio of a central ablation depth and anablation depth in a defined area, or the difference and/or ratio ofminimum or maximum ablation depth in defined areas.
 38. The processorreadable storage device of claim 33, wherein the step of determiningwhether the actual volumetric profile is within specified tolerancesfurther comprises determining whether the actual volumetric profilecorresponds to the desired refractive correction.
 39. The processorreadable storage device of claim 35, wherein the basic theoretical modelis a toric or nontoric thin lens formula.
 40. The processor readablestorage device of claim 39, wherein an amount of correction in dioptersand/or an optical zone of the thin lens formula is modified successivelyto approximate the theoretical volumetric profile to the actualvolumetric profile.
 41. The processor readable storage device of claim40, wherein the modification step of the amount of correction indiopters is one of ±1.0 D, ±0.5 D, ±0.33 D or ±0.25 D.
 42. The processorreadable storage device of claim 40, wherein the modification step ofthe optical zone is one of 1.00 mm, 0.75 mm, 0.50 mm or 0.25 mm.
 43. Theprocessor readable storage device of claim 33, wherein the specifiedtolerance is a fixed tolerance, preferably at least one of a tolerateddeviation in sphere, cylinder, axis, and optical zone.
 44. The processorreadable storage device of claim 33, wherein the specified tolerance isa minimal tolerance, preferably by optimizing the tolerated deviation insphere, cylinder, axis and optical zone to provide the minimal deviationfrom the actual volumetric profile.
 45. The processor readable storagedevice of claim 33, wherein the processor readable storage device is afloppy disk, flexible disk, hard disk, magnetic tape, CD-ROM, DVD,magnetic medium, optical medium, physical medium, RAM, PROM, EPROM, orFLASH-EPROM.